1. Field of the Invention
Aspects of the present invention relate to an organic light emitting display and a method of manufacturing the same, and more particularly, to an organic light emitting display and a method of manufacturing the same that can reduce the number of the masks needed and improve production yield by forming alignment marks during an SGS crystallization process for producing a thin film transistor.
2. Description of the Related Art
Generally, an organic light emitting element is a self-emissive display device which emits light by electrically excited fluorescent and/or phosphorescent materials when holes are injected into an anode and electrons are injected into a cathode.
FIG. 1 is a cross-sectional diagram illustrating a conventional organic light emitting element. Referring to FIG. 1, an organic light emitting element includes an anode (ITO; Indium Tin Oxide), an organic thin film (or organic light emitting film), and a cathode (Metal). The organic thin film has a multi-layered structure including an emitting layer (EML) to emit light when an electron (−) and a hole (+) are combined to form an exciton, an electron transport layer (ETL) to transport electrons (−) and a hole transport layer (HTL) to transport holes (+). Further, an electron injecting layer (EIL) to inject electrons (−) can be formed on one side of the electron transport layer (ETL), and a hole injecting layer (HIL) to inject holes (+) can be formed on one side of the hole transport layer (HTL).
A driving technique of the organic light emitting element includes a passive matrix (PM) technique and an active matrix (AM) technique. The passive matrix technique is driven by forming anodes and cathodes to be orthogonal to each other and selecting lines connected to the anodes and the cathodes. The passive matrix driving type organic light emitting element is advantageous because of a relatively simple manufacturing process and inexpensive coat but consumes a large amount of power when implementing a large sized display. The active matrix technique includes an active element such as a thin film transistor (TFT) and a capacitive element on each pixel. The active matrix driving type is advantageous because of low power consumption, high image quality, long life, and large sized displays.
Generally, a method of manufacturing an organic light emitting device includes forming a thin film transistor and forming an organic light emitting element. Of course, the method may include an encapsulating process, a module process, and other processes. Explanation of such processes, however, will be omitted.
The manufacturing method of the thin film transistor includes cleaning a substrate, forming a buffer layer, depositing an amorphous silicon, crystallizing to form a polycrystalline silicon, patterning, forming a gate insulating layer, patterning a gate, ion implantation/activation, forming an interlayer insulating layer, forming a contact, patterning source/drain, forming a insulating layer and a via, forming ITOs, and forming a pixel definition film.
Generally, each process of the manufacturing method of the thin film transistor is performed using a separate mask as an alignment mark on a surface of the substrate, a surface of the buffer layer, or a surface of the insulating layer so that it is carried out at the correct positions of the substrate. Particularly, the crystallization to form the thin film transistors needs an alignment mark for position control in order to improve the properties of the resultant thin film transistors. Accordingly, the manufacturing method of the thin film transistor further includes forming the alignment mark.
In addition, the manufacturing method of the organic light emitting display includes a cleaning process, a pre-treating process, a deposition process of the organic light emitting element, and a deposition process of a cathode, etc. A separate operation of forming the alignment mark for position control is generally carried out in each of the separate operations. In other words, a separate operation of forming the alignment mark also is generally carried out in each operation of the manufacturing of the organic light emitting element.
As described above, since a separate process of forming the alignment mark is carried out in the conventional process of manufacturing the organic light emitting display, an additional mask is required. Accordingly, the manufacturing process is more complicated. In addition, if the alignment mark deviates from the correct position beyond a permissible level, inferior goods are produced in subsequent processes, and thus, production yield is reduced substantially.